Control of calcined petroleum coke particle size

ABSTRACT

THE PARTICLE SIZE OF CALCINED PETROLEUM COKE PRODUCT CAN BE CONTROLLED BY EITHER (1) CONTACTING COKE WITH 2-21 MOLE PERCENT OXYGEN ATMOSPHERE AT ABOUT 450-600*F. FOR 1/2-16 HOURS TO PREVENT AN INCREASE IN PARTICLE SIZE DURING LATER CALCINING, OR (2) HIGH VOLATILE PETROLEUM COKE FINES CAN BE CONSOLIDATED BY CALCINING THEM AT FROM ABOUT 1800 TO ABOUT 3000*F. FOR ABOUT 1/2 TO ABOUT 2 HOURS UNDER AN ATMOSPHERE SUBSTANTIALLY FREE FROM OXYGEN.

Jan. 23, 1973 v, R D 3,712,855

CONTROL OF CALCINED PETROLEUM COKE PARTICLE SIZE Filed May 6, 1970 4 Sheets-Sheet 1 I00 l I I l ROBINSON DELAYED coKE TREATMENT TIME: 2 HRS.

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CONTROL OF CALCINED PETROLEUM COKE PARTICLE SIZE Filed May 6, 1970 4 Sheets-Sheet 4 AIR m THERMOCOUPLE OFF-GAS OUT WITNESSES INVENTOR Z VICTOR 0. ALLRED t z v United States Patent 3,712,855 CONTROL OF CALCINED PETROLEUM COKE PARTICLE SIZE Victor D. Allred, Littleton, Colo., assignor to Marathon Oil Company, Findlay, Ohio Filed May 6, 1970, Ser. No. 34,965

Int. Cl. 01% 53/08 US. Cl. 201--6 7 Claims ABSTRACT OF THE DISCLOSURE The particle size of calcined petroleum coke product can be controlled by either 1) contacting coke with 2-21 mole percent oxygen atmosphere at about 450-600 F. for /a16 hours to prevent an increase in particle size during later calcining, or (2) high volatile petroleum coke fines can be consolidated by calcining them at from about 1800 to about 3000 F. for about /2 to about 2 hours under an atmosphere substantially free from oxygen.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention pertains to the field of petroleum coke, and to the calcining thereof and might be classified under Class 201, distillation: processes, thermolytic, subclass 9 and surface treating material to reduce or prevent agglomerating or foaming or swelling during distillation or in Class 201, subclass 42, Particle Size.

(2) Description of the prior art Various methods for controlling the properties of cokes have been described, e.g. US. 2,998,354 which increases the density of fluid coke particles. Controlled atmospheres during coking and calcining have been taught by e.g. US. 3,271,268 and US. 870,271. The control of agglomeration of carbonaceous materials has been taught by US. 2,755,234 and US. 3,032,477 and British Pat. 770,930. Calcining apparatus has been taught by US. 3,227,627, US. 3,470,068 and by Martin, S. W. and Guthrie, Virgil B., Petroleum Products Handbook, McGraw Hill (1960), particularly Section 14. Various other patents within the general field of heat treatment of carbonaceous materials are US. 2,560,767, US. 2,998,354, US. 2,964,464, US. 1,564,730, US. 3,032,477; US. 3,337,417. Various processes for producing petroleum coke are discussed by Bland, William F. and Davidson, Robert L. in the Petroleum Processing Handbook, McGraw Hill (1967) Section 3-67 through 3-74 in Chapter 3.

SUMMARY (1) General statement of the invention Control of particle size and the corresponding particle density is of particular importance where petroleum coke is to be used for electrodes, resistors, and carbon shapes. The present invention embodies the discovery that, by treating petroleum coke, preferably delayed petroleum coke having selected volatile content, with gases which contain specific levels of oxygen content at temperatures in the range of from about 450 to about 600 F., the coke may be prevented from consolidating during subsequent calcination. Alternatively, by calcining without said pretreatment and conducting the calcining under an atmosphere containing substantially no free oxygen, finer coke particles can be caused to consolidate, yielding a calcined product which has a higher average particle size than the raw coke being fed. In short, consolidation or agglomeration can be controlled by varying the degree of oxygenation of the coke.

3,712,855 Patented Jan. 23, 1973 (2) Utility of the invention The invention provides control of particle size during calcining of petroleum coke. The principal use of such coke isin the production of shapes which are graphitized by heating to much higher temperatures, e.g. according to the techniques described in US. 3,460,907 and Mantel, Carbon and Graphite Handbook, Chapters 15-22 and the references cited therein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vector diagram showing relationship be tween pretreatment temperature, volatile matter, and oxygen content.

FIG. 2 is a graph of the relationship between pretreatment time and oxygen uptake on the agglomerating properties of coke.

FIG. 3 is a graph showing the relationship between average particle size of the initial and final materials after oxygen pretreatment and before calcining.

FIG. 4 is a schematic diagram of laboratory apparatus used for the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Starting materials The starting materials for the present invention are petroleum cokes, e.g. those made by either the delayed or the fluid coking processes as described in Chapter 3 of the aforementioned Petroleum Processing handbook. Delayed petroleum coke is particularly preferred. Volatile content of the dry coke used in practicing the invention should be 10 to 20, more preferably 12 to 15, and most preferably 13 to 14 weight percent.

(2) Pretreatment-Apparatus The coke may be contacted with the gas stream in any convenient solid-liquid contactor, e.g. those shown in Perry, Chemical Engineers Handbook 4th ed. (1963), e.g. static-bed systems, such as various dryers where the solids rest on a perforate surface with the gases moving perpendicular to the bed, tunnel dryers, continuous through-circulation conveyor dryers; moving bed systems, e.g. rotary kilns, the Roto-Louvre dryer manufactured by Link Belt Company, various shaft type dryers and coolers in which moving bed systems flow by gravity, the multilouvre dryer of Link Belt Company, various conveyor systems in which the material is contacted with cocurrent, countercurrent or perpendicular gas flow, e.g. harmonic motion conveyors, screen type conveyor belts; fluidizedbed systems, e.g. cyclones, Flue-Solids reactor manufactured by Dorr-Oliver, Inc., various fluidized bed dryers and other pneumatic systems. A wide variety of these are shown in Perrys Chemical Engineers Handbook, 4th ed. 1963, Chapter 20. FIG. 4 shows a simple laboratory-type contactor in which the gas stream is preheated in a coil and fed through a bed of carbon lying in a container having a gas-tight lid. This apparatus is convenient for laboratory pretreatment.

(3) Composition of the pretreatment gas stream According to the invention, to prevent agglomeration the carbonaceous materials is contacted with an oxygencontaining gas stream consisting primarily of air or free oxygen in inert gases, e.g. N C0, C Ar, He, and H 0 vapor prior to calcination. Contact between the coke and the oxygen-containing atmosphere must be reasonably intimate and it is preferable that the coke bed move gently during the period of contact with the gas.

Alternatively to assure agglomeration of fines, it is necessary to calcine the coke in an atmosphere substantially free of oxygen, and also to prevent prolonged heating, even in the presence of an inert gas in the temperature range of 900-l300 F.

(4) Pretreatment contact time The contact time between the coke and the gas stream will be from about 0.3 to about 20, more preferably from 0.4 to about 2, and most preferably from 0.5 to about 1.0 hours. If the carbonaceous material is not spread sufficiently thin to provide good gas-solid contact, longer times will be required.

(5) Pretreatment temperature The temperature of the gases contacting the carbonaceous material to prevent agglomeration will be from 350 to about 700, more preferably from 450 to about 650, and more preferably from 450 to about 500 F. In general, it is preferred that the carbonaceous material be at approximately the same temperature and this can readily be accomplished by conventional preheating. However, if necessary, the coke can be brought into contact with the gases at lower coke temperatures with the coke being gradually heated by contact with the hot gas stream.

(6) Pretreatment oxygen content In cases where the particle size of the product is to be approximately that of the feed (that is, Where agglomeration is to be avoided), the oxygen content during pretreatment will be from about 2 to about 30, more preferably from 4 to about 25, and most preferably about 21% by volume of the gas stream with care being taken to avoid spontaneous ignition by too high a percent oxygen.

FIG. 1 shows the oxygen content versus pretreatment at various temperatures for a typical delayed coke. FIG. 2 shows the eeffct of various intervals of pretreatment with oxygen-containing gas on the degree of oxygen percent and indicates the difference between agglomerating and non-agglomerating characteristics for a typical high volatile delayed coke.

FIG. 3 shows the results of treatment of reasonably typical high volatile petroleum coke in air for periods of 1 to 16 hours at a temperature of 500 F.

Data for FIGS. 1 through 3 were obtained by techniques similar to those employed in the examples which follow.

(7) Calcining apparatus and conditions The apparatus used for calcining according to the present invention can generally be that taught by the references discussed under the description of the prior art, above, except that where the desired particle size is the same as or larger than that of the raw coke being fed to the calciner, apparatus which minimizes the amount of agitation will be preferred. Especially preferred for such purposes will be the apparatus of the aforementioned US. Pat. 3,227,627.

At its col. 3, lines 3-15, this patent teaches oxidizing the volatile material in an upper portion of the devolatilizing chamber to radiate heat onto the material on the hearth. In its FIG. 2 and col. 4, lines -16 it describes a bed of coal 7 being coked upon the substantially imperforate hearth 2 wherein the particles on the hearth are in contacting support with each other. As taught at its col. 5, lines 14-15, this bed may be formed of materials other than coal, e.g., the petroleum coke of the present application (see also col. 1, line 27 of US. 3,227,- 627).

For agglomeration the oxygen content during calcination will be from 0.00 to about 0.10, most preefrably 0.00. Where agglomeration is to be avoided, the oxygen content during calcination is not narrowly critical but will probably range from about 0. to about 5%, more preferably from 0. to about 4%, and most preferably as low as possible.

(8) Examples The invention will be better understood by reference to the following example which should be considered as being illustrative only.

EXAMPLE I Preventing agglomeration according to the invention Referring to FIG. 4, delayed petroleum coke produced from vacuum residuum type hydro-carbon feed stock by the method as discussed in Mantel, Carbon and Graphite Handbook, pp. 149-151, crushed to a particle size of minus 20 mesh Tyler Sieve Size is contacted with the air stream containing 21% 05 in a tray-type dryer in which the coke is spread onto trays and the gas stream flows across the stacked trays. The temperature of the gas stream is held at about 500 F. and the contact is maintained for approximately minutes. At the end of this time the coke is removed from the trays of the dryer and is calcined in a 50 ml. crucible for about 30 minutes at about 1800 F. in a mutfie furnace. The volatile content of the coke prior to drying is 14.2%, after drying is essentially the same, and after calcining is about 1% by Weight based on the Weight of the raw dry coke. Average particle size after calcining is approximately the same or less than before pretreatment, indicating that no substantial agglomeration has occurred.

EXAMPLE II Agglomeration according to the invention When coke identical to that used in Example I is calcined identically with the procedures of Example I, under an atmosphere which has an oxygen content of less than about 0.1% by volume, the finished volatile content is as stated in Example 1. However, the product particle size is essentially that of the 50 ml. crucible in which the coke was calcined, indicating that substantial agglomeration has taken place, fusing all the coke into a cohesive mass.

EXAMPLE III Preventing agglomeration according to the invention When delayed petroleum coke having a particle size distribution and volatile content similar to that of Example II, above, is pretreated with the air stream of Example I in a Linkbelt Roto louver Dryer and calcined in the apparatus shown in US. 3,475,286 according to the techniques of Example I, the particle size distribution of the product is approximately the same or smaller than before treatment due to thermal shrinkage, and no substantial agglomeration occurs.

EXAMPLE IV Agglomeration not according to the invention When coke identical to that of Example III is calcined in the substantial absence of oxygen, according to the techniques of Example III, but without the pretreatment with the gas stream, the product size distribution is approximately as in Example II, indicating that substantial agglomeration has occurred.

(9) Modifications of the invention It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto. For example, mixtures of the carbonaceous materials discussed above may be utilized, various combinations of the apparatus described above or apparatus of novel configuration may be utilized, provided that it accomplishes the desired gas contact and/or calcining.

What is claimed is:

1. In a process for the production of calcined petroleum coke having an average particle size of from to about 15,000 microns and a volatile content of from 1 to about 0.01% by weight based on the weight of the calcined coke, the improvement comprising intimately contacting coke of the normally agglomerating variety having an average particle size of from about 10 to about 50,000 microns and a volatile content of from 10 to about 25% by weight based on the weight of the dry coke with a gas stream containing from 2 to about 30% by volume free oxygen, the remainder of said gas stream being gases substantially non-reactive with said coke, at a tempera ture of from about 450 to about 600 F. for a period of from 0.3 to about hours and thereafter calcining said coke at a temperature of from about 1800 to about 3000 F. for from about 0.25 to about 4 hours to produce a coke having an average particle size of from about 10 to about 15,000 microns, wherein the coke is calcined in a furnace having a substantially imperforate hearth located in a lower portion of a chamber, which supports a bed of said coke during said contact, and wherein said particles are in contacting support with each other and wherein a substantial portion of the volatiles emitted from said coke during said calcining are burned in a combustion zone in an upper portion of said chamber away from contact with said coke, whereby heat from said combustion zone is directed onto said coke to cause further calcination.

2. The process of claim 1 wherein the coke is contacted with said oxygen-containing gas at a temperature of from about 500 to about 550 F. for a time of from about 0.5 to about 2.0 hours and wherein said calcining is accomplished at a coke temperature of from about 1800 to about 2500 F. for a time of from about 0.8 to about 8 hours.

3. The process of claim 2 wherein said coke is delayed petroleum coke.

4. In a process for the production of calcined petroleum coke having an average particle size of. from 100 to about 50,000 microns and a volatile content of from 1 to about 0.01 percent by weight based on the weight of the calcined coke, the improvement comprising calcining and simultaneously agglomerating coke having an average particle size of from about 10 to about 3,000 microns and a volatile content of from 10 to about 25% by weight based on the weight of the carbon in said coke in contact with gases containing from 0.00 to about 0 .10% by volume free oxygen, the remainder of said gases being substantially non-reactive with said coke, at a temperature of from about 1800 to about 3000 F. for a period of from 0.33 to about 48 hours, wherein the coke is contacted with said gases in a furnace having a substantially imperforate hearth which supports a bed of said coke during said contact wherein said coke particles are in contacting support with each other, and a combustion chamber suspended over said hearth and wherein a substantial portion of the volatiles emitted from said coke during said calcining are burned in a combustion zone located away from contact with said coke, whereby heat from said combustion zone is reflected onto said coke to cause further calcination.

5. The process of claim 2 wherein the coke is calcined in contact with said gases in a by-product coke oven having long, narrow refractory chambers in which the coke is calcined by the combustion of a fuel gas in lines built into the walls of said refractory chambers.

6. The process of claim 2 wherein the coke is calcined in contact with said gases at a temperature of from about 1800 to about 2400 F. for a time of from about 0.2 to about 24 hours.

7. The process of claim 6 wherein said coke is delayed petroleum coke.

References Cited UNITED STATES PATENTS 3,448,012 6/1969 Allred 201-27 2,805,189 9/1957 Williams 201-9 1,775,323 9/1930 Runge 201-9 3,047,472 7/1962 Gorin et a1. 201-9 2,658,862 11/ 1953 Hornet 201-42 2,710,280 6/ 1955 Borch 202- X NORMAN YUDKOFF, Primary Examiner D. EDWARDS, Assistant Examiner U.S. Cl. X.R. 

